Reaming instrument with adjustable profile

ABSTRACT

A reaming instrument, in accordance with one embodiment, includes a rotatable cutting head and a cutting face on a distal end of the cutting head. At least one radially displaceable cutting element has a cutting edge projecting in a distal direction from the cutting face. An adjustment element is operable to displace the cutting element toward a fully retracted state, or toward a fully expanded state. In another embodiment, a method of modifying a bone surface includes displacing at least one cutting element on a reamer instrument to a fully retracted state, inserting the instrument into a human or animal, operating an adjustment element to displace the cutting element toward an expanded state, and activating the cutting head to begin cutting the bone.

FIELD

The present invention relates generally to minimally invasive surgicalinstrumentation, and more particularly to a minimally invasive reaminginstrument with an adjustment element that permits adjustment of theinstrument's profile.

BACKGROUND

Joint arthroplasty procedures, sometimes referred to as “jointreplacements”, are commonly performed to relieve pain, restore mobilityor address other issues caused by injury or degenerative conditions in ajoint. Many types of arthroplasty procedures involve a partial or totalreplacement of the joint with prosthetic implants. In a total jointarthroplasty, the ends of the bones that are adjacent the joint to bereplaced are cut away, or partially removed, to prepare and reshape thebone surface so that a prosthetic implant can be securely attached tothe bone surface. This process of removing or reshaping the bone isoften done with a tool referred to as a “reamer”.

Certain joints, such as the glenohumeral joint (i.e. “shoulder joint”),are surrounded by bones and tissue, making it difficult to access thejoint in a minimally invasive procedure. To access these joints with areamer, the surgeon may have little choice but to make a large incisionthat accommodates the full profile size of the reamer. Large incisionscan traumatize tissue, increase the risk of complications, and take along time to fully heal.

SUMMARY

Applicants have developed reamers in accordance with the invention thatfeature an adjustable profile. The adjustable profile allows the profileof the reamers to be minimized, so that the reamers can be insertedthrough very small incisions and navigated through tissue in a minimallyinvasive manner.

In one beneficial aspect of the invention, a reaming instrument with anadjustable profile can include a rotatable cutting head having aproximal end, a distal end and an axis of rotation about which thecutting head is rotatable. A cutting face can be positioned on thedistal end of the cutting head, the cutting face conforming to a planeextending generally perpendicular to the axis of rotation. At least oneradially displaceable cutting element can have a cutting edge thatprojects in a distal direction from the cutting face. An adjustmentelement can be operably engaged with the at least one radiallydisplaceable cutting element. The adjustment element can be operable ina first operation to displace the at least one radially displaceablecutting element radially inwardly with respect to the axis of rotation,and toward a fully retracted state in which the cutting head has aminimum cutting head profile. The adjustment element can also beoperable in a second operation to displace the at least one radiallydisplaceable cutting element radially outwardly with respect to the axisof rotation, and toward a fully expanded state in which the cutting headhas a maximum cutting head profile.

In another beneficial aspect of the invention, the adjustment elementcan include a first engagement surface, and the at least one radiallydisplaceable cutting element can include a second engagement surface.

In another beneficial aspect of the invention, the first engagementsurface can be in direct contact with the second engagement surface.

In another beneficial aspect of the invention, the reaming instrumentcan have an adjustment element having a gear wheel with a firstplurality of gear teeth.

In another beneficial aspect of the invention, the reaming instrumentcan have a gear wheel that defines a central bore having a bore axis.

In another beneficial aspect of the invention, the reaming instrumentcan have a gear wheel that defines a central bore, where the centralbore is substantially parallel to and substantially coaxial with theaxis of rotation of the cutting head.

In another beneficial aspect of the invention, the reaming instrumentcan have a gear wheel that defines a central bore that defines an innerwall, the inner wall having a hexagonal profile to form a hexagonalsocket inside the gear wheel.

In another beneficial aspect of the invention, the reaming instrumentcan have at least one radially displaceable cutting element having asecond plurality of gear teeth configured to mate with the firstplurality of gear teeth on the gear wheel.

In another beneficial aspect of the invention, the reaming instrumentcan have at least one radially displaceable cutting element having arack, the rack having a second plurality of gear teeth.

In another beneficial aspect of the invention, the reaming instrumentcan have at least one radially displaceable cutting element having anL-shaped body defining a first leg and a second leg extending in adirection generally perpendicular to the first leg.

In another beneficial aspect of the invention, the reaming instrumentcan have at least one radially displaceable cutting element having arack, wherein the rack extends along a second leg of the cuttingelement.

In another beneficial aspect of the invention, the reaming instrumentcan have at least one radially displaceable cutting element having acutting edge that projects from a first leg of the cutting element.

In another beneficial aspect of the invention, the reaming instrumentcan have a plurality of cutting elements projecting in the distaldirection from the cutting face, with at least one radially displaceablecutting element being one of the plurality of cutting elements.

In another beneficial aspect of the invention, the reaming instrumentcan have a plurality of cutting elements that are uniformly spaced fromone another on the cutting face.

In another beneficial aspect of the invention, the reaming instrumentcan have at least one radially displaceable cutting element with acutting edge, at least a portion of the cutting edge projecting radiallyoutwardly from a perimeter edge of the cutting face when the at leastone radially displaceable cutting element is in a fully expanded state.

In another beneficial aspect of the invention, the reaming instrumentcan have at least one radially displaceable cutting element with acutting edge, the cutting edge extending, in its entirety, inside aperimeter edge of the cutting face when the at least one radiallydisplaceable cutting element is in a fully retracted state.

In another beneficial aspect of the invention, the reaming instrumentcan have a first radially displaceable cutting element having a firstcutting edge, and a second radially displaceable cutting element havinga second cutting edge. The first radially displaceable cutting elementcan be movable in a first radial direction toward the fully expandedstate, and the second radially displaceable cutting element can bemovable in a second radial direction toward the fully expanded state,the second radial direction being opposite the first radial direction.The reaming instrument can have a cutting face that is generallycircular, with the second radially displaceable cutting elementangularly offset from the first radially displaceable cutting element byan angle of approximately 180 degrees with respect to the generallycircular cutting face. The first radially displaceable cutting elementand the second radially displaceable cutting element can both beoperably engaged with an adjustment element.

In another beneficial aspect of the invention, the reaming instrumentcan have a first radially displaceable cutting element having a firstcutting edge, a second radially displaceable cutting element having asecond cutting edge, a third radially displaceable cutting elementhaving a third cutting edge, and a fourth radially displaceable cuttingelement having a fourth cutting edge. The third radially displaceablecutting element can be movable in a third radial direction toward afully expanded state, and the fourth radially displaceable cuttingelement can be movable in a fourth radial direction toward the fullyexpanded state, the fourth radial direction being opposite the thirdradial direction. The first, second, third and fourth radiallydisplaceable cutting elements can be angularly offset from one anotherby an angle of approximately 90 degrees. The third radially displaceablecutting element and the fourth radially displaceable cutting element canboth be operably engaged with the adjustment element.

In another beneficial aspect of the invention, the reaming instrumentcan include a drill bit centrally located on the cutting face. Inaddition, the cutting face can define at least one slot that extendsthrough the cutting face. A portion of at least one radiallydisplaceable cutting element can extend within the at least one slot,with the at least one slot defining a path of travel for the radiallydisplaceable cutting element as the radially displaceable cuttingelement is displaced between a fully expanded state and a fullyretracted state.

In another beneficial aspect of the invention, the reaming instrumentcan include a drive shaft extending from the cutting head, the driveshaft operable to rotate the cutting head during a bone cuttingprocedure.

In another beneficial aspect of the invention, the reaming instrumentcan include an adjustment tool extending from an adjustment element, theadjustment tool configured to actuate the adjustment element in a firstoperation to displace at least one radially displaceable cutting elementradially outwardly with respect to an axis of rotation, toward a fullyexpanded state, the adjustment tool also configured to actuate theadjustment element in a second operation to displace the at least oneradially displaceable cutting element radially inwardly with respect tothe axis of rotation, toward a fully retracted state.

In another beneficial aspect of the invention, the reaming instrumentcan include a drive shaft that defines a hollow passage in its interior,and wherein the adjustment tool extends through the hollow passage ofthe drive shaft. The adjustment tool can be rotatable independently ofthe drive shaft.

In another beneficial aspect of the invention, a method of modifying asurface of a bone in a human or animal includes selecting a reaminginstrument having: (1) a rotatable cutting head comprising a proximalend, a distal end and an axis of rotation about which the cutting headis rotatable; (2) a cutting face positioned on the distal end of thecutting head, the cutting face conforming to a plane extending generallyperpendicular to the axis of rotation; (3) at least one radiallydisplaceable cutting element having a cutting edge, the cutting edgeprojecting in a distal direction from the cutting face; and (4) anadjustment element operably engaged with the at least one radiallydisplaceable cutting element. The adjustment element can be operable ina first operation to displace the at least one radially displaceablecutting element radially inwardly with respect to the axis of rotation,and toward a fully retracted state in which the cutting head has aminimum cutting head profile. The adjustment element can also beoperable in a second operation to displace the at least one radiallydisplaceable cutting element radially outwardly with respect to the axisof rotation, and toward a fully expanded state in which the cutting headhas a maximum cutting head profile.

In another beneficial aspect of the invention, the method of modifying asurface of a bone in a human or animal can include operating theadjustment element in a first operation to displace the at least oneradially displaceable cutting element radially inwardly with respect tothe axis of rotation, to the fully retracted state.

In another beneficial aspect of the invention, the method of modifying asurface of a bone in a human or animal can include inserting the reaminginstrument into the human or animal.

In another beneficial aspect of the invention, the method of modifying asurface of a bone in a human or animal can include navigating thereaming instrument to a space around the surface of the bone.

In another beneficial aspect of the invention, the method of modifying asurface of a bone in a human or animal can include positioning thecutting face in a desired orientation and position to begin cutting thebone surface.

In another beneficial aspect of the invention, the method of modifying asurface of a bone in a human or animal can include operating theadjustment element in a second operation to displace the at least oneradially displaceable cutting element radially outwardly with respect tothe axis of rotation.

In another beneficial aspect of the invention, the method of modifying asurface of a bone in a human or animal can include activating thecutting head to begin cutting the bone.

In another beneficial aspect of the invention, the method of modifying asurface of a bone in a human or animal can include deactivating thecutting head to stop cutting the bone.

In another beneficial aspect of the invention, the method of modifying asurface of a bone in a human or animal can include operating theadjustment element in a first operation to displace the at least oneradially displaceable cutting element radially inwardly with respect tothe axis of rotation, to a fully retracted state.

In another beneficial aspect of the invention, the method of modifying asurface of a bone in a human or animal can include withdrawing thereaming instrument from the human or animal while maintaining the atleast one radially displaceable cutting element in the fully retractedstate.

BRIEF DESCRIPTION OF THE DRAWINGS

The summary and detailed description sections will be better appreciatedwhen reviewed in conjunction with the drawing figures. The followingdrawing figures illustrate exemplary and non-limiting embodiments of theinvention, and depict elements which can be combined and arranged eitheras shown, or in other combinations and arrangements that arecontemplated by persons of skill in the art.

FIG. 1 is a perspective view of a reamer and power tool in accordancewith one embodiment of the invention;

FIG. 2 is a side view of the reamer of FIG. 1;

FIG. 3 is a cross section view of the reamer of FIG. 2;

FIG. 4 is an enlarged exploded perspective view of components at one endof the reamer of FIG. 2;

FIG. 4A is an enlarged perspective view of one of the cutting elementsat one end of the reamer of FIG. 2;

FIG. 5 is an end view of the reamer of FIG. 2, showing a minimizedprofile of the cutting head as it would appear in a fully retractedstate;

FIG. 6 is an end view of the reamer of FIG. 2, showing a maximizedprofile of the cutting head as it would appear in a fully expandedstate;

FIG. 7 is an exploded perspective view of the reamer of FIG. 2;

FIG. 8 is an enlarged perspective view of a component of the reamer ofFIG. 2;

FIG. 9 is a block diagram describing one possible method of using areamer in accordance with the invention;

FIG. 10 is an enlarged perspective view of components at one end of thereamer of FIG. 2, with an optional drill bit attached to the cuttinghead of the reamer; and

FIG. 11 is an enlarged exploded perspective view of components of areamer in accordance with an alternative embodiment.

DETAILED DESCRIPTION

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

Embodiments of the invention are described in this section in thecontext of how they could be used in a shoulder arthroplasty in humans,and more specifically in the preparation of bone surfaces on the glenoidportion of the scapula and the humerus. These descriptions are providedwith the understanding that embodiments of the invention can also beused on other joints, and are not limited to shoulder arthroplastyprocedures. For example, the disclosed embodiments, and otherinstruments in accordance with the invention, can be used for preparingbone surfaces in joints in human wrists, fingers, hips, knees, ankles,toes and the spine. Moreover, embodiments of the invention can be usedfor boring, reaming or planing bone surfaces, or other procedures forpreparing bone surfaces. For simplicity, the following description willrefer to embodiments of the invention as “reamers” regardless of howthey are used.

Reamers in accordance with preferred embodiments of the invention allowfor insertion of the reamer in a minimally invasive manner. This can beaccomplished by utilizing an adjustable insertion “profile”. The term“profile”, as used herein, means the size of an object's footprint orshape, from an end view perspective. This definition of “profile”applies to any component or section of an instrument, but will be mainlyused in this description in describing the cutting head of aninstrument. When used in this manner, the profile of a cutting headmeans the footprint or shape of the cutting head from an end view of thecutting head. Profiles of cutting heads will be described in more detailin conjunction with embodiments described herein.

The profile of cutting heads in accordance with the invention can beadjustable in a variety of configurations. In general, the profile ofinstruments can be adjustable to at least two possible configurations:(1) a fully retracted or collapsed state, and (2) a fully expandedstate. The term “fully retracted state” means a state in which theprofile of the cutting head is minimized and occupies the least amountof lateral space. The term “fully expanded state” means a state in whichthe profile of the cutting head is maximized and occupies the greatestamount of lateral space. In some embodiments, the cutting head may alsobe adjustable to one or more partially expanded state(s). A “partiallyexpanded state” means a state in which the profile of the cutting headis neither minimized nor maximized, with an adjustable portion of thecutting head positioned somewhere between the positions it would occupyin the fully retracted and fully expanded states. In a partiallyexpanded state, that the cutting head's profile is larger than theprofile the cutting head assumes in the fully retracted state, butsmaller than the profile the cutting head assumes in the fully expandedstate.

Referring to FIGS. 1-3, a reamer 100 is shown in accordance with onepossible embodiment of the invention. Reamer 100 has a proximal end 102,which can be directly handled or manipulated by a surgeon during asurgical procedure, and a distal end 104, which represents the end thatis inserted into a patient. Proximal end 102 and distal end 104 areseparated from one another by a hollow outer shaft, or “drive shaft” 120that defines an interior space 121. Drive shaft 120 is connected to arotatable cutting head 200 at distal end 104 of reamer 100.

Cutting head 200 has a proximal end 202 and a distal end 204 oppositethe proximal end of the cutting head. Proximal end 202 of cutting head200 connects with a distal end 122 of drive shaft 120. In particular,proximal end 202 of cutting head 200 defines a socket 203 having aninternal geometry that receives a plug end 124 at distal end 122 ofdrive shaft 120. Socket 203 defines a rounded non-circular passage, anda rear wall 205. Inner shaft 300 is configured to be inserted intosocket 203 with plug end 124 adjacent to or in proximity to rear wall205. Plug end 124 is further configured to rotate in socket 203 and lockinto a pair of apertures that extend through the wall of the socket. Aswill be described, the connection between cutting head 200 and driveshaft 120 allows the cutting head and drive shaft to rotate in unisonwhen power is supplied to rotate the drive shaft. During rotation,cutting head 200 is rotatable about an axis of rotation “X”.

Referring now to FIGS. 2-6, distal end 204 of cutting head 200 includesa cutting face 210. Cutting face 210 has a generally flat planar surface211 that conforms to a cutting face plane “Y” shown in FIGS. 2 and 3.Cutting face plane Y extends generally perpendicular to axis of rotationX. As such, cutting face 210 is oriented to provide a cutting direction“D” generally parallel to axis of rotation X. Cutting face 210 has aperimeter edge 212 that conforms to a circle “C”. Circle C has a centerpoint “P” that intersects axis of rotation X.

Cutting heads in accordance with the invention can have one or morecutting elements arranged on the cutting face. The number of cuttingelements on the cutting face, and the spatial arrangement of cuttingelements on the cutting face, can depend on factors including but notlimited to the type of procedure being performed and/or the particularbone surface being prepared.

Cutting head 200 includes a total of eight cutting elements 220A-220Hthat project from cutting face 210 in a distal direction. Each cuttingelement forms a raised section on cutting face 210. Cutting elements220A-220H are arranged in a radial array on cutting face 210. That is,cutting elements 220A-220H appear in a circular pattern on cutting face210 when the cutting face is viewed in the direction of axis of rotationX, shown in FIG. 5. In this arrangement, each of cutting elements220A-220H is angularly offset from adjacent cutting elements aboutcenter point P by an angle of ⊖ as shown. The angular offset ⊖ betweenadjacent cutting elements is preferably the same, i.e. approximately 45degrees, so that the cutting elements are uniformly spaced from oneanother. Each of cutting elements 220A-220H defines a cutting edge 221.

Referring to FIG. 4A, cutting elements 220A-220H each have an elongatedcutting section 222 extending in a generally radial direction betweencenter point P and perimeter edge 212. Each cutting section 222 has afirst side 223, a second side 224 opposite the first side, and a thirdside 225 that interconnects the first side and second side. Second side224 projects farther out in a distal direction from cutting face 210than first side 223. As such, third side 225 defines a ramped surface226 that gradually extends away from cutting face 210 as the rampedsurface progresses in a counterclockwise direction CCW between theplanes of the first side and second side, as shown.

Cutting head 200 has an adjustable profile that allows the cutting headto assume a fully retracted state, a fully expanded state and apartially expanded state. The profile of cutting head 200 is adjustableby virtue of cutting elements 220A and 220E, which are radiallydisplaceable with respect to cutting face 210. That is, cutting elements220A and 220E are displaceable toward or away from center point P ofcutting face 210 and the axis of rotation X. The remaining cuttingelements, i.e. 220B, 220C, 220D, 220F, 220G and 220H are fixed withrespect to cutting face 210.

Cutting elements 220A and 220E can be displaced radially inwardly withrespect to the axis of rotation X, to the fully retracted state shown inFIG. 5. In this state, each of the cutting elements 220A and 220E andtheir respective cutting edges extend in their entirety inside perimeteredge 212 of cutting face 210, with the cutting face having a minimumcutting face profile. This profile produces a cut having the smallestdiameter.

Cutting elements 220A and 220E can also be displaced radially outwardlywith respect to the axis of rotation X, to the fully expanded stateshown in FIG. 6. In this state, at least a portion of cutting elements220A and 220E and their respective cutting edges project radiallyoutwardly from perimeter edge 212 of cutting face 210, with the cuttingface having a maximum cutting face profile. This profile produces a cuthaving the largest diameter.

Cutting head 200 includes an adjustment element for adjusting the radialposition of the radially displaceable cutting elements 220A and 220E.Adjustment elements in accordance with the invention can take variousforms. For example, cutting head 200 includes an adjustment element inthe form of a gear wheel 240 contained inside an interior space 201inside cutting head 200. Gear wheel 240 has a ring shaped body 241 thatdefines a bore 242. Bore 242 has a central bore axis 243 that issubstantially parallel to and substantially coaxial with axis ofrotation X of cutting head 210. In addition, bore 242 defines an innerwall 247, the inner wall having a hexagonal profile that forms ahexagonal socket 244 inside the gear wheel. Ring shaped body 241 has afirst engagement surface 245 defining a first plurality of gear teeth246 that extend radially outwardly from the ring shaped body.

Gear wheel 240 operably engages cutting elements 220A and 220E tofacilitate radial displacement of those cutting elements. Cuttingelements 220A and 220E each have an L-shaped body 230 defining a firstleg 230A and a second leg 230B extending in a direction generallyperpendicular to the first leg. L-shaped bodies 230 are configured forinsertion into similarly shaped L-shaped slots 216 in cutting head 200.Each slot 216 adjoins interior space 201 inside cutting head 200 anddefines two slot sections, a first slot section 216A and a second slotsection 216B. Slot sections 216A are defined in and extend throughcutting face 210, and slot sections 216B are defined in and extendthrough the outer circumference of cutting head 200.

Each first leg 230A includes a cutting section 222 and cutting edge 221projecting outwardly from cutting face 210 when cutting head 200 isassembled. Each first leg 230A is configured to project through one ofthe first slot sections 216A, with its respective cutting section 222projecting from cutting face 210. Cutting sections 222 associated withcutting elements 220A and 220E preferably project from cutting face 210by the same distance that the fixed cutting elements 220B, 220C, 220D,220F, 220G and 220H project from the cutting face.

Second legs 230B extend through slot sections 216B and into interiorspace 201. Each second leg 230B features a second engagement surface 232in the form of a rack 234. Rack 234 includes a second plurality of gearteeth 236. The second plurality of gear teeth 236 directly contact andmate with the first plurality of gear teeth 246 on gear wheel 240. Theengagement between the first plurality of gear teeth 246 on gear wheel240, and the second plurality of gear teeth 236 on cutting elements 220Aand 220E, facilitates radial adjustment of cutting elements 220A and220E to change the cutting head profile to the fully retracted state,fully expanded state or a partially expanded state. By rotating gearwheel 240, rotational force is converted to linear force through theracks to expand and retract cutting elements 220A and 220E, and therebyadjust the cutting face profile.

Cutting element 220A is angularly offset from cutting element 220E by anangle of approximately 180 degrees with respect to circle C. Inaddition, cutting elements 220A and 220E are oriented with their secondlegs and cutting sections generally parallel to one another. In thisarrangement, cutting element 220A is movable in a first radial directiontoward the fully expanded state, and cutting element 220E is movable ina second radial direction toward the fully expanded state, the secondradial direction being opposite the first radial direction.

Cutting elements 220A and 220E have identical configurations, and aremated with gear wheel 240 so that the gear wheel engages correspondingsections on each of the cutting elements at any one time. In thisarrangement, the cutting edges of cutting elements 220A and 220E areequidistant from center point P of cutting face 210 at any time duringadjustment of the cutting face profile.

Adjustment elements in accordance with the invention can be coupled to,or permanently attached to, an adjustment tool. Referring to FIGS. 3 and7, for example, gear wheel 240 is coupled to an adjustment tool having ahexagonal shaped inner shaft 300. Inner shaft 300 extends inside driveshaft 120 and into hexagonal socket 244 in gear wheel 240. A distal end304 of inner shaft 300 has an exterior geometry that matches thegeometry of inner wall 247 inside hexagonal socket 244. In thisarrangement, gear wheel 240 is rotatable in response to rotation ofinner shaft 300 when the inner shaft is inserted into hexagonal socket244. Preferably, gear wheel 240 and inner shaft 300 share a common axisof rotation that is coaxial with axis of rotation X, as shown in theFigures.

Reamer 100 can ream bone surfaces when cutting head 200 is in the fullyretracted state, or when the cutting head is in the fully expandedstate, or when the cutting head is in a partially expanded state. Asopposed to designs that fold back portions of the cutting face, orotherwise move sections of the cutting face out of the cutting faceplane to reduce the profile of the cutting head, reamer 100 is designedso that all cutting edges on cutting face 210 remain in cutting faceplane Y in all modes of operation. In particular, the cutting edges oncutting elements 220A and 220E remain in cutting face plane Y so thatthey are available for reaming bone in in the fully retracted state, thefully expanded state and any partially expanded state. This allows theprofile of cutting head 200 to be reduced without sacrificing thereaming function of the cutting head when the profile is reduced. Bykeeping cutting elements 220A and 220E in cutting face plane Y in allstates, the reamer offers a variable adjustable cutting face thatprovides a range of cutting face diameters.

Drive shaft 120 can be driven manually or by a driver tool such as adrill. Referring again to FIGS. 1-3 and 7, reamer 100 includes a drillattachment element 130 that allows a driver tool 600 to control rotationof drive shaft 120 and cutting head 200. Drill attachment element 130has a proximal end 132 and a distal end 134. Proximal end 132 has acoupling element 133 that can be clamped into the chuck of a drill.Distal end 134 is connected with a barrel 140 by a pair of rods 138.Barrel 140 has a proximal end 142, a distal end 144 and a bore 143extending between the proximal and distal ends of the barrel. Bore 143receives drive shaft 120 in a fixed arrangement. A pair of diametricallyopposed pins 146 extend through a first pair of diametrically opposedholes 148 in barrel 140, and a second pair of diametrically opposedholes 126 in drive shaft 120. Pins 146 lock drive shaft 120 and barrel140 together so that the drive shaft and barrel are rotatable in unison.

Distal end 134 of drill attachment element 130 defines a cut section 135that extends around approximately one half of the circumference of thedistal end. Similarly, proximal end 142 of barrel 140 defines a cutsection 145 that extends around approximately one half of thecircumference of the proximal end. When drill attachment element 130 andbarrel 140 are joined end to end, cut sections 135 and 145 align withone another to form a circumferential slot 147 that extends aroundapproximately one half of the circumference of the drill attachmentelement and barrel.

The connection between drill attachment element 130 and barrel 140 ishoused inside a ring shaped sleeve 160. Sleeve 160 overlaps the junctionbetween drill attachment element 130 and barrel 140. A hole 162 extendthrough sleeve 160 and aligns with circumferential slot 147.

A number of different mechanisms can be employed in accordance with theinvention to operate the cutting head generally, and more specificallyto control the adjustment element during adjustment of the cutting headprofile. Referring to FIGS. 2 and 7, reamer 100 includes an actuatorassembly 400 located toward proximal end 102. Actuator assembly 400includes a collar 410 that is fixed to inner shaft 300 inside sleeve160. Collar 410 includes a bore 412 that receives inner shaft 300 in afixed arrangement, and a stem 414 that extends in a radially outwarddirection. Stem 414 is positioned so that it aligns with and extendsthrough circumferential slot 147. In addition, stem 414 extends throughhole 162 in sleeve 160.

Actuator assembly 400 also includes a push button 420. Push button 420has a cylindrical extension 422 that extends through hole 162 in sleeve160, and through circumferential slot 147. A spring 430 is positionedover stem 414 and fits inside cylindrical extension 422 with the stem. Asmall tab 424 extends from cylindrical extension 422. Tab 424 isreceived in a groove 148 located in cut section 145 of barrel 140.Groove 148, which is shown best in FIG. 8, has a main section 149 andfive side slots 151A-151E that extend radially outwardly from the mainsection.

Push button 420, sleeve 160, collar 410 and inner shaft 300 arerotatable in unison with respect to the axis of the inner shaft. In thisarrangement, push button 420 can be rotated with respect to the axis ofinner shaft 300 to rotate gear wheel 240 and adjust the position ofcutting elements 220A and 220E. Spring 430 exerts a biasing force onpush button 420 to bias the push button in a radially outward direction.This biasing force urges tab 424 to enter one of the side slots151A-151E in groove 148. Each of side slots 151A-151E represents a stopposition along groove 148 that prevents tab 424 from traveling along thegroove. When tab 424 is captured in one of side slots 151A-151E, theposition of push button 420 is locked relative to barrel 140, preventingrotation of gear wheel 240. Each of side slots 151A-151E therebycooperates with tab 424 to form a locking mechanism 170 that locks andholds the position of cutting elements 220A and 220E in a desiredposition or setting, with each side slot corresponding to a differentposition or setting for cutting elements 220A and 220E.

Actuator assemblies in accordance with the invention can feature avariety of locking mechanisms that offer any number of settings. Lockingmechanism 170 provides five settings, allowing cutting elements 220A and220E to be locked in five different positions, or degrees of expansion,with respect to cutting face 210. Main section 419 of groove 418 forms apath of travel 421 for tab 424. Path of travel 421 spans an arccorresponding to an angle of 120 degrees. Side slots 151A-151E areincrementally spaced along path of travel 421. In this arrangement, eachof side slots 151A-151E is angularly offset from an adjacent side slotby an angle of 30 degrees.

Side slot 151A corresponds to the fully retracted state, in whichcutting elements 220A and 220E are not expanded at all with respect tocutting face 210. In this position, cutting head 200 has a cuttingdiameter of approximately 20 mm. Slot 151B corresponds to a firstpartially expanded state, in which cutting elements 220A and 220E areradially expanded with respect to cutting face 210, and in which cuttinghead 200 has a cutting diameter of approximately 23 mm. Slot 151Ccorresponds to a second partially expanded state, in which cuttingelements 220A and 220E are radially expanded further with respect tocutting face 210, with cutting head 200 having a cutting diameter ofapproximately 26 mm. Slot 151D corresponds to a third partially expandedstate, in which cutting elements 220A and 220E are radially expandedeven further with respect to cutting face 210, with cutting head 200having a cutting diameter of approximately 29 mm. Lastly, slot 151Dcorresponds to the fully expanded state, in which cutting head 200 has acutting diameter of approximately 32 mm.

Referring again to FIG. 3, all of the components of reamer 100 definehollow passages that share a common longitudinal axis aligned with axisof rotation X. The hollow passages interconnect and collectively form asingle through-passage 110. Through-passage 110 allows reamer 100 to bepassed over a guide wire, guide pin or other means for guiding aninstrument to a desired location in a patient.

Referring to FIG. 9, a method for using a reaming instrument inaccordance with the invention is described in block diagram form. Theblock diagram in FIG. 9 depicts steps that could be performed indifferent sequences, and/or supplemented with other steps notrepresented in the Figure. Certain steps represented in FIG. 9 can alsobe repeated one or more times in a procedure. Therefore, the stepsdepicted in FIG. 9 are not intended to represent the only possiblesequence of steps that is contemplated.

In step 500, the profile of the cutting head is minimized by moving theradially displaceable cutting elements radially inwardly. In this state,the profile of cutting the head is minimized so that a minimal incisionis required to insert the cutting head through the patient's tissue andinto proximity of the shoulder joint. This step can obviously be skippedif the cutting head is already adjusted to the fully retracted state.

In step 510, the reamer is inserted into the patient and advanced towardthe shoulder joint while the cutting head is maintained in the fullyretracted state. Once cutting head reaches a desired position to engagea bone surface, the profile of the cutting head is set in step 520. Insetting the profile, the user can keep the radially displaceable cuttingelements in the same position so that the cutting head has a minimumprofile, or can adjust the radially displaceable cutting elements.Therefore, the term “set” as used herein in the context of the cuttinghead profile means keeping the position of the radially displaceablecutting elements in place without moving them, or adjusting the radiallydisplaceable cutting elements to another position. If the user intendsto adjust the radially displaceable cutting elements, the user canoperate the adjustment tool to displace the radially displaceablecutting elements until the cutting head is in a partially expanded stateor the fully expanded state.

Once the profile of the cutting head is set, the reamer is activated torotate the cutting head and begin preparing the surface of the bone instep 530. One or more steps can be completed for preparing the bonesurface, which may include shaving or otherwise removing bone materialwith one or more cutting head profiles used at a single location, or atmultiple locations. Once the user is finished with the reaminginstrument, the user deactivates the reamer in step 540. The user canthen adjust the cutting head to the fully retracted state by retractingthe adjustable cutting elements in step 550. Once the cutting head is inthe fully retracted state, the user can remove the instrument from thepatient in step 560.

A method of operating a reamer in accordance with the invention will nowbe described in more detail. To better visualize the steps, the methodwill refer to components of reamer instrument 100, with theunderstanding that the method could also describe the manner ofoperating other instrument configurations and arrangements in accordancewith different embodiments of the invention.

A user, such as a surgeon or other party responsible for administering asurgical procedure, inserts inner shaft 300 through drive shaft 120 andinto hexagonal socket 244 of gear wheel 240, so that the inner shaft isengaged with the gear wheel. Obviously, this step can be skipped or maynot be applicable if inner shaft 300 is already attached to gear wheel240. At this stage, push button 420 is positioned in a radially outwardposition under the bias of spring 430, so that tab 424 is engaged in oneof side slots 151A-151E in a locked condition.

The actuator assembly 400 is utilized to minimize the profile of thecutting head 200 prior to inserting the reamer 100 into a patient. Tominimize the profile of cutting head 200, the user can disengage thelocking mechanism and move cutting elements 220A and 220E to the fullyretracted state. To accomplish this, the user depresses push button 420,i.e. pushes the push button radially inwardly on the instrument, so thattab 424 is displaced out of the side slot and into main section 419 ofgroove 418. In this position, tab 424 is free to move along the path oftravel 421, thereby allowing push button 420, collar 410, sleeve 160 andinner shaft 300 to rotate. While holding down push button 420 in thedepressed position, the user rotates the push button in a firstdirection to rotate inner shaft 300. As inner shaft 300 rotates, theinner shaft rotates gear wheel 240. Gear wheel 240, in turn, displacescutting elements 220A and 220E along slots 216. Cutting elements 220Aand 220E are displaced radially inwardly toward center point P. Pushbutton 420 is rotated in the first direction until tab 424 reaches oneend of the path of travel 421, at which time, further rotation in thefirst direction is not possible. In this stopped condition, cutting head200 is in the fully retracted state. The fully retracted state can bevisually confirmed by observing the position of cutting elements 220Aand 220E, which should be inside perimeter edge 212 of cutting face 210.The profile of cutting head 200 is therefore minimized so that thecutting head can fit through a minimal incision and be navigated throughthe patient's tissue into proximity of the shoulder joint, all in aminimally invasive manner.

Tab 424 is radially aligned with side slot 151A when cutting elements220A and 220E reach the fully retracted state. Push button 420 can bereleased at this stage. Releasing push button 420 releases stored energyin spring 430 and pushes the push button and tab 424 radially outwardly.As push button moves radially outwardly, tab 424 enters side slot 151A,where it locks inner shaft 300, and cutting elements 220A and 220E inthe fully retracted state. Gear wheel 240 preferably engagescorresponding locations on racks 234 on cutting elements 220A and 220E,as noted earlier. Therefore, cutting elements 220A and 220E retractsimultaneously and reach the fully retracted state at the same time.

Reamer 100 is inserted into the patient and advanced toward the shoulderjoint while cutting head 200 is maintained in the fully retracted state.Once cutting head 200 reaches a desired position to engage a bonesurface, reamer 100 can be activated to rotate cutting head 200 andbegin preparing the surface of the bone, for example by shaving the bonesurface. As such, cutting head 200 can be utilized to prepare the bonesurface even when the cutting head is in the fully retracted state.Cutting head 200 makes the smallest diameter cut made when the cuttinghead is in the fully retracted state.

If a larger diameter cut is desired, locking mechanism 400 can bedisengaged, and push button 420 rotated in a second direction oppositethe first direction, to expand cutting elements 220A and 220E into oneof the other four positions. For example, push button 420 can be rotatedin the second direction relative to drive shaft 120 to rotate gear wheel240 and expand cutting elements 220A and 220E radially outwardly to thefirst, second, or third partially expanded state. To accomplish this,push button 420 is depressed and rotated until tab 424 aligns with oneof side slots 151B, 151C or 151D.

Alignment between tab 424 and side slots 151A-151E can be confirmedusing markings or other indicia on the exterior of the instrument whichindicate the relative positions of the tab and side slots.Alternatively, alignment can be confirmed by using tactile feedback, acombination of markings and tactile feedback, or other means. Sleeve 160includes an arrow shaped marking 161 that can be rotated into alignmentwith one of five lines 141 on barrel 140. Arrow shaped marking 161corresponds to the radial position of tab 424, and each of lines 141corresponds to the radial position of one of side slots 151A-151E. Oncetab 424 is aligned with one of side slots 151B, 151C or 151D, pushbutton 420 is released, thereby releasing stored energy in spring 430.Spring 430 returns push button 420 to the undepressed state and movestab 424 into one of side slots 151B, 151C or 151D, locking cuttingelements 220A and 220E in one of the partially expanded states.

If a maximum diameter cut is desired, inner shaft 300 can be rotatedfurther in the second direction to rotate gear wheel 240 and expandcutting elements 220A and 220E radially outwardly to the fully expandedstate. In this state, the diameter of any cut would be maximized. Toaccomplish this, push button 420 is depressed and rotated until tab 424aligns with side slot 151E. Once tab 424 is aligned with side slot 151E,push button 420 is released. Spring 430 returns push button 420 to theundepressed state and moves tab 424 into side slot 151E, locking cuttingelements 220A and 220E in the fully expanded state.

Depending on the type of procedure, reamer 100 can be used to make aseries of cuts of different sizes, all in the same location, or indifferent locations, while the reamer is inserted into the shoulderjoint. For example, reamer 100 can be operated with cutting head 200 inthe fully expanded state to produce a shallow cut having a relativelylarge diameter. Then, without moving reamer 100 from the location of thecut, the profile of cutting head 200 can be reduced by rotating innershaft 300 in the second direction to retract cutting elements 220A and220E. Once cutting elements 220A and 220E are retracted to the desiredpositions, cutting can be resumed to produce a deeper section with asmaller diameter. This combination of cuts, or other combinations, canbe performed to produce complex surface preparations that featuredifferent diameters at different depths within the bone.

Once the bone surface is prepared at a specific location, reamer 100 caneither be moved to a different location to prepare another bone surface,or be removed from the patient. In either case, the user can reduce theprofile of cutting head 200 to the fully retracted state, prior tomoving the cutting head. Cutting head 200 occupies the smallest profilein the fully retracted state, so that minimal contact or interferencewith surrounding bone or tissue occurs while the cutting head isnavigated to other bone surfaces, or while reamer 100 is withdrawn fromthe patient.

Referring now to FIG. 10, cutting head 200 is shown with an optionaldrill bit 250 attached to cutting face 210. Drill bit 250 can be used acentering guide to stabilize and control cutting head 200 as the cuttingface 210 advances into a bone surface. For example, drill bit 250 can bedriven into a pilot hole to guide cutting head 200 so that the cuttinghead remains stable and follows the desired cutting path. Drill bit 250is cannulated, i.e. the drill bit defines a hollow central passage 252like inner shaft 300, gear wheel 240 and other components of reamer 100to allow the drill bit and the rest of the assembly to be advanced overa guide wire, guide pin or other guide means.

Thus far, examples have been described and illustrated that feature tworadially displaceable cutting elements. Reamers in accordance with theinvention need not feature two radially displaceable cutting elements,as other reamers having fewer or more displaceable cutting elements arealso contemplated to be within the scope of the invention. For example,reamers in accordance with the invention can feature a cutting head withonly one radially displaceable cutting element. One example could havethe same identical arrangement as reamer 100, but instead of having twodisplaceable cutting elements 220A and 220E and two slots 216 in cuttinghead, the cutting head would have only one displaceable cutting element,e.g. the cutting element corresponding with cutting element 220A, andone slot. The cutting element corresponding to cutting element 220Ewould appear identical to any of the fixed cutting elements 220B, 220C,220D, 220F, 220G or 220H, and the one of the slots 216 would not bepresent in the cutting head.

Reamers in accordance with the invention can also feature a cutting headwith more than two radially displaceable cutting elements. Referring nowto FIG. 11, a cutting head 2000 having four radially displaceablecutting elements is shown. In particular, cutting head 2000 includesfour radially displaceable cutting elements 2200A, 2200C, 2200E and2200G, and four fixed cutting elements 2200B, 2200D, 2200F and 2200H,uniformly arranged on a cutting face 2100. Many of the features ofcutting head 2000 are similar, if not identical, to features of cuttinghead 200.

Each of the radially displaceable cutting elements 2200A, 2200C, 2200Eand 2200G has an L-shaped body 2300 defining a first leg 2300A and asecond leg 2300B extending in a direction generally perpendicular to thefirst leg. L-shaped bodies 2300 are configured for insertion intosimilarly shaped L-shaped slots 2160 in cutting head 2000. Each slot2160 adjoins an interior space 2010 inside cutting head 2000 and definestwo slot sections, a first slot section 2160A and a second slot section2160B. Each slot section 2160A is defined in and extends through cuttingface 2100, and each slot section 2160B is defined in and extends throughthe outer circumference of cutting head 2000.

Each first leg 2300A includes a cutting section 2220 and cutting edge2210 projecting outwardly from cutting face 2100. Cutting head 2000 alsoincludes an adjustment element in the form of a gear wheel 2400 housedin interior space 2010. Gear wheel 2400 has a cylindrical shaped body2410 with an axial length that is slightly longer than gear wheel 240.Body 2410 defines a bore 2420 and features a first engagement surface2450. First engagement surface 2450 defines a first plurality of gearteeth 2460 that extend radially outwardly from body 2410.

Second legs 2300B of radially displaceable cutting elements 2200A,2200C, 2200E and 2200G extend through slot sections 2160B and intointerior space 2010. Each second leg 2300B features a second engagementsurface 2320 in the form of a rack 2340. Rack 2340 includes a secondplurality of gear teeth 2360. The second plurality of gear teeth 2360directly contact and mate with the first plurality of gear teeth 2460 ongear wheel 2400. The engagement between the first plurality of gearteeth 2460 and second plurality of gear teeth 2360 facilitates radialadjustment of cutting elements 2200A, 2200C, 2200E and 2200G to adjustthe cutting head profile to the fully retracted state, fully expandedstate or a partially expanded state.

Cutting elements 2200A, 2200C, 2200E and 2200G are angularly offset fromone another by an angle of approximately 90 degrees with respect to acenter point P. First legs 2300A associated with cutting elements 2200Cand 2200G are slightly longer that the first legs associated withcutting elements 2200A and 2200E, but all cutting edges 2210 projectfrom cutting face 2100 by the same distance. In this arrangement, secondlegs 2300B associated with cutting elements 2200C and 2200G arepositioned proximally with respect to the second legs associated withcutting elements 2200A and 2200E, so that the paths of displacement ofcutting elements 2200A and 2200E do not intersect and obstruct the pathsof displacement of cutting elements 2200C and 2200G.

While preferred embodiments of the invention have been shown anddescribed herein, it will be understood that such embodiments areprovided by way of example only. Numerous variations, changes andsubstitutions will occur to those skilled in the art without departingfrom the scope of the invention.

For example, drive shaft 120, cutting head 200 and inner shaft 300 areshown and described in the drawing figures with substantially rigidtubular bodies. Drive shafts, cutting heads and inner shafts inaccordance with the invention may also incorporate one or more flexiblesections made up of interlocking sections that allow the components torotate and flex, as described in U.S. Pat. No. 8,366,559 by the sameinventors, the content of which is incorporated by reference herein inits entirety. For example, drive shafts, cutting heads, inner shafts andother components in accordance with the invention can be constructedwith Applicants' flexible shaft being sold or licensed under thetrademark FLEXMETRIC™.

In addition, cutting heads in accordance in the invention need not havethe same number, arrangement and/or type of cutting elements describedand illustrated in the drawing figures. For example, cutting heads inaccordance with the invention can include as few as one cutting element,and as many as 10, 12, 14 or more cutting elements. The cutting elementsneed not be uniformly spaced from one another in a radial array, but canbe randomly dispersed on a cutting face.

Moreover, reamers in accordance with the invention can have any numberof settings or positions for the radially displaceable cutting elements.For example, radially displaceable cutting elements in accordance withthe invention can be set to three positions: a fully retracted position,a fully expanded position, and one partially expanded position inbetween the fully retracted position and fully expanded position.Embodiments that use grooves and side slots to adjust the setting, thegroove would feature three side slots, with each side slot correspondingto one of the settings. This embodiment would feature a barrel similarto barrel 140, but having a groove with only three side slotscorresponding to side slots 151A, 151C and 151E, for example. It will beunderstood to those skilled in the art that other embodiments canfeature more side slot, so as to offer more settings, and smallerincremental adjustments. For example, a reamer in accordance with theinvention may feature a barrel with 7 side slots along an arc-shapedgroove, each side slot being angularly offset by an angle of 20 degrees.The amount of incremental adjustment can be controlled as a function ofeach angular offset, relative tab size, relative side slot size andother variables. The total range of adjustment can be controlled as afunction of arc length, which may be lesser or greater than 120 degrees.

Furthermore, components of reamers in accordance with the invention canhave relative dimensions, shapes and configurations that deviatesignificantly from components shown in the drawing figures. For example,socket 203 on cutting head 200 is shown with a relatively long axiallength in comparison to the axial length of the cutting elements.Although the drawings are not necessarily to scale, socket 203 can bemuch shorter than the length shown in the drawing figures, and still beable to connect with drive shaft 120. A shorter axial length reduces theoverall size and mass of the reamer, and therefore be desirable incertain applications In addition, plug end 124 may have a differentgeometry and mechanism for coupling with socket 203. For example, plugend 124 may have one or more detents on the side of the plug end thatcooperate with slots inside socket 203 in a bayonet-type connection. Inthe bayonet-type connection, the plug end can be coupled to the cuttinghead by inserting the plug end in the socket, with the detents in theslots, and then twisting the plug end to lock the plug end in thesocket.

Accordingly, it is intended that the appended claims cover all suchvariations as fall within the spirit and scope of the invention.

What is claimed:
 1. A reaming instrument with an adjustable profile, thereaming instrument comprising: a rotatable cutting head comprising aproximal end, a distal end and an axis of rotation about which thecutting head is rotatable; a cutting face positioned on the distal endof the cutting head, the cutting face conforming to a plane extendinggenerally perpendicular to the axis of rotation; at least one radiallydisplaceable cutting element having a cutting edge, the cutting edgeprojecting in a distal direction from the cutting face; and anadjustment element operably engaged with the at least one radiallydisplaceable cutting element, the adjustment element being operable in afirst operation to displace the at least one radially displaceablecutting element radially inwardly with respect to the axis of rotation,and toward a fully retracted state in which the cutting head has aminimum cutting head profile, the adjustment element also being operablein a second operation to displace the at least one radially displaceablecutting element radially outwardly with respect to the axis of rotation,and toward a fully expanded state in which the cutting head has amaximum cutting head profile.
 2. The reaming instrument of claim 1,wherein the adjustment element comprises a first engagement surface, andthe at least one radially displaceable cutting element comprises asecond engagement surface.
 3. The reaming instrument of claim 2, whereinthe first engagement surface is in direct contact with the secondengagement surface.
 4. The reaming instrument of claim 1, wherein theadjustment element comprises a gear wheel having a first plurality ofgear teeth.
 5. The reaming instrument of claim 4, wherein the gear wheeldefines a central bore having a bore axis.
 6. The reaming instrument ofclaim 5, wherein the central bore is substantially parallel to andsubstantially coaxial with the axis of rotation of the cutting head. 7.The reaming instrument of claim 5, wherein the central bore defines aninner wall, the inner wall having a hexagonal profile to form ahexagonal socket inside the gear wheel.
 8. The reaming instrument ofclaim 5, wherein the at least one radially displaceable cutting elementcomprises a second plurality of gear teeth configured to mate with thefirst plurality of gear teeth on the gear wheel.
 9. The reaminginstrument of claim 8, wherein the at least one radially displaceablecutting element comprises a rack, and the rack comprises the secondplurality of gear teeth.
 10. The reaming instrument of claim 9, whereinthe at least one radially displaceable cutting element has an L-shapedbody defining a first leg and a second leg extending in a directiongenerally perpendicular to the first leg.
 11. The reaming instrument ofclaim 10, wherein the rack extends along the second leg.
 12. The reaminginstrument of claim 10, wherein the cutting edge of the at least oneradially displaceable cutting element projects from the first leg. 13.The reaming instrument of claim 1, wherein the cutting face comprises aplurality of cutting elements projecting in the distal direction fromthe cutting face, the at least one radially displaceable cutting elementbeing one of the plurality of cutting elements.
 14. The reaminginstrument of claim 13, wherein the plurality of cutting elements areuniformly spaced from one another on the cutting face.
 15. The reaminginstrument of claim 1, wherein at least a portion of the cutting edge ofthe at least one radially displaceable cutting element projects radiallyoutwardly from a perimeter edge of the cutting face when the at leastone radially displaceable cutting element is in the fully expandedstate.
 16. The reaming instrument of claim 1, wherein the cutting edgeof the at least one radially displaceable cutting element extends, inits entirety, inside a perimeter edge of the cutting face when the atleast one radially displaceable cutting element is in the fullyretracted state.
 17. The reaming instrument of claim 1, wherein the atleast one radially displaceable cutting element comprises a firstradially displaceable cutting element having a first cutting edge, and asecond radially displaceable cutting element having a second cuttingedge.
 18. The reaming instrument of claim 17, wherein the first radiallydisplaceable cutting element is movable in a first radial directiontoward the fully expanded state, and the second radially displaceablecutting element is movable in a second radial direction toward the fullyexpanded state, the second radial direction being opposite the firstradial direction.
 19. The reaming instrument of claim 17, wherein thecutting face is generally circular, and the second radially displaceablecutting element is angularly offset from the first radially displaceablecutting element by an angle of approximately 180 degrees with respect tothe generally circular cutting face.
 20. The reaming instrument of claim17, wherein the first radially displaceable cutting element and thesecond radially displaceable cutting element are both operably engagedwith the adjustment element.
 21. The reaming instrument of claim 17,wherein the at least one radially displaceable cutting element furthercomprises a third radially displaceable cutting element having a thirdcutting edge, and a fourth radially displaceable cutting element havinga fourth cutting edge.
 22. The reaming instrument of claim 21, whereinthe third radially displaceable cutting element is movable in a thirdradial direction toward the fully expanded state, and the fourthradially displaceable cutting element is movable in a fourth radialdirection toward the fully expanded state, the fourth radial directionbeing opposite the third radial direction.
 23. The reaming instrument ofclaim 21, wherein the first, second, third and fourth radiallydisplaceable cutting elements are angularly offset from one another byan angle of approximately 90 degrees.
 24. The reaming instrument ofclaim 21, wherein the third radially displaceable cutting element andthe fourth radially displaceable cutting element are both operablyengaged with the adjustment element.
 25. The reaming instrument of claim1, wherein the cutting face comprises a drill bit centrally located onthe cutting face.
 26. The reaming instrument of claim 1, wherein thecutting face defines at least one slot that extends through the cuttingface.
 27. The reaming instrument of claim 26, wherein a portion of theat least one radially displaceable cutting element extends within the atleast one slot, the at least one slot defining a path of travel for theat least one radially displaceable cutting element as the at least oneradially displaceable cutting element is displaced between the fullyexpanded state and the fully retracted state.
 28. The reaming instrumentof claim 1 comprising a drive shaft extending from the cutting head, thedrive shaft operable to rotate the cutting head during a bone cuttingprocedure.
 29. The reaming instrument of claim 28 comprising anadjustment tool extending from the adjustment element, the adjustmenttool configured to actuate the adjustment element in the first operationto displace the at least one radially displaceable cutting elementradially outwardly with respect to the axis of rotation, toward thefully expanded state, the adjustment tool also configured to actuate theadjustment element in the second operation to displace the at least oneradially displaceable cutting element radially inwardly with respect tothe axis of rotation, toward the fully retracted state.
 30. The reaminginstrument of claim 29, wherein the drive shaft defines a hollow passagein its interior, and wherein the adjustment tool extends through thehollow passage of the drive shaft.
 31. The reaming instrument of claim30, wherein the adjustment tool is rotatable independently of the driveshaft.
 32. A method of modifying a surface of a bone in a human oranimal, the method comprising the steps of: A. selecting a reaminginstrument having: (1) a rotatable cutting head comprising a proximalend, a distal end and an axis of rotation about which the cutting headis rotatable; (2) a cutting face positioned on the distal end of thecutting head, the cutting face conforming to a plane extending generallyperpendicular to the axis of rotation; (3) at least one radiallydisplaceable cutting element having a cutting edge, the cutting edgeprojecting in a distal direction from the cutting face; and (4) anadjustment element operably engaged with the at least one radiallydisplaceable cutting element, the adjustment element being operable in afirst operation to displace the at least one radially displaceablecutting element radially inwardly with respect to the axis of rotation,and toward a fully retracted state in which the cutting head has aminimum cutting head profile, the adjustment element also being operablein a second operation to displace the at least one radially displaceablecutting element radially outwardly with respect to the axis of rotation,and toward a fully expanded state in which the cutting head has amaximum cutting head profile, B. operating the adjustment element in thefirst operation to displace the at least one radially displaceablecutting element radially inwardly with respect to the axis of rotation,to the fully retracted state; C. inserting the reaming instrument intothe human or animal; D. navigating the reaming instrument to a spacearound the surface of the bone; E. positioning the cutting face in adesired orientation and position to begin cutting the bone surface; F.operating the adjustment element in the second operation to displace theat least one radially displaceable cutting element radially outwardlywith respect to the axis of rotation; and G. activating the cutting headto begin cutting the bone.
 33. The method of claim 32, furthercomprising the steps of: H. deactivating the cutting head to stopcutting the bone; I. operating the adjustment element in the firstoperation to displace the at least one radially displaceable cuttingelement radially inwardly with respect to the axis of rotation, to thefully retracted state; and J. withdrawing the reaming instrument fromthe human or animal while maintaining the at least one radiallydisplaceable cutting element in the fully retracted state.